Protection of wells



Oct- 14`, 1958 T. o. ALLEN ETAL 2,856,001

PROTECTION oF WELLS Filed Deo. 24, 195e '9 INVENToRs. THOMAS 0. ALLEN, JOHN C. McDUFFIE JR..

BY JOHN O. MINTERI United States Patent PROTECTION F v WELLS Thomas. Allen, Bellaire, and John C. McDufe, Jr., and John 0.'Mi'1`1ter, Thompsons, Tex., assignors, by mesne assignments, to .lersey Production Research Company Application'DecemberM, 1956,-.Serial No. 630,312

11. Claims; (Cl. 166-22) The'present invention is directed to a method for protection of Wells. More particularly the invention is concerned with the placement of a protective iiuid in an exposed area in a well bore.A In its more specific aspects, theinvention is concerned with the protection of perforations in a Well casing following which an operation is performed in the well'.

The present invention may be briefly described as a method for protecting an exposed area `or perforations in a well having tubing arranged therein or in a well casing with Vthe lower open end of the tubing maintained at a'level a substantial distance above the exposed area or`the perforations in the well casing. In the present invention the Well lhas penetrated a hydrocarbon pro ducinginterva'l or zone and the Well is filled with Well iluidsl such as oil,v gas and water from the productive zone, strata, interval, horizon, sand, formation, and the like'. In the practice of the, present invention the tubing maintained at the particular level has introduced into it at 'the well head a low fluid loss emulsion or gel which has the property of forming a cohesive body. The emulsionis owed out of the lower end of the tubing to form the' cohesive body in and to lill the area and toextend in an elongated form fromv the lower end of the tubing through the well uids, separate and distinct from the well iluids, to the area to be protected. TheY introduction of the emulsion or gel is discontinued and the well fluids are displaced from the well up the annular space between the tubing and the wall of the well. The cohesive body remains. in and protects the exposed arca during the displacement of the well uids while the tubing is maintained with its lower end at the level. It is contemplated that the tubing will be maintained in place in the practice of the present invention with its lower open end at a level from about 50 to 1000 feet above the exposed area or zone which is to be protected. Thus, the fluids employed for protection form a continuous and cohesive body without discontinuities in the placement thereof and flow downwardly as if directed in a conning channel such as a ,pipe or tubing. rl`his is a valuable property of the protective uids since it allows and con.-V tributes to the obtaining vof the advantages of this invention.

The emulsion or gel isy suitably placed iny the tubing at the well headv and then pumped downwardly by a workover lluid free of gas, following which the uid free of gas' may be employed to displace the well fluids from the-annular space in the well. Subsequent kto the displacement of the well fluids from the well, operations may be performed in the well or well casing such as repairing leaking tubings and the like. For example, a leaking tubing may then be removed from the well, repaired or replaced with a tube free of leaks following which the cohesive body is rem-oved from the area by providing a pressure differential into the well bore which causes'the cohesive body to be ilowed from the protected area or interval of the casing and from the well. Thererifice 2 after, hydrocarbons are again produced from the area which was protected inthe well bore.

The lowuid loss uid, gel, or emulsion employed in thev practice. of the present invention may suitably be a fluid .such as an emulsion of an oily phase'and a water phase and the like.y Suitable materials have been amply described in SerialNo. 567,604, filed February 24, 1956, for Bryan E. Morgan and Gerald G. Priest. The fluids describedv in. Serial No. 567,604 are eminently suitable in theY practice of the present invention and comprise a stableV emulsion of an oily medium and an aqueous medium which has a controllable density, the density of the emulsion beingV adjusted by dissolving a weighting agent in one of the phases of the emulsion to produce a solids-free emulsion. Other suitable protective fluids are describedlinnpending application Serial No. 630,266, filed December 24, 1956, for Gerald G. Priest,.Bryan E. Morganand BertieF. Birdwell, in which an emulsion of an oily phase. and an aqueous phase is described and claimed, the emulsion in Serial No. 630,266 being a stable. emulsionv employing as an emulsifying agent a water-soluble salt of purified lignin sulfonic acid or a water-soluble salt vof lignin sulfonic acid containing a certain amount of ash and reducing sugars. Other fluids suitable in thepractice'of the present invention are describedin Serial No. 630,026, entitled Well Completion Fluids, andV filedDecernber 24, 1956, for Gerald G. Priest, Bryan El Morgan, Melba L. Lytle, Bertie F. Birdwell andloseph A. Caldwell. In Serial No. 630,026 a heat stable, non-.corrosive emulsion is described and claimed in which an emulsifying agent is employed and in which the oily phase of theemulsion comprises a substantial amount of tetrachloroethylene, with oneV of the phases ofthe emulsion containinga corrosion inhibitor. These several low iltration loss fluids described in the. several applications have the characteristic of low filtration rate and further the characteristic of maintaining perforations-open and exposed areas in wells protected without damaging or injuring the permeability and porosity of the formationfor interval with; which they come into contact. ln short, the low uid loss fiuids suitable for use in the present invention have the characteristic of lo-W filtration rate and of resisting entrance of other fluids into perforations in or into an earth formation. ln addition, these iiuids, particularly those described in the several applications, do not damage a formation or sand and the like with which they come into Contact. These low iluid loss iiuids, gels, or emulsions have the further property of forming a cohesive mass whichy does not readily substantially intermingleormix with -other liuids such aswell fluids as exemplified by oil, gas, water and the like. The iiuids or emulsions employed suitably have a low iluid lo-ss, a weight at least equal to that of the normalworking uids employed for blowoutprotection in wells and are free of constituents which might permanently plug the formation or casing perforations. Thus, the iluids used in the practice of this invention block ingress of damaging fluids fromthe well to the formation but allow lluids from the formation to flow into. the well bore on adjustment of the differential pressure into the well bore.

ln the present invention a method is provided for protecting a productive Zoney in a Well without-lowering the tubing to the productive zone and without running` a tubing extension which would eifectively extend the tubing to the producing zone. The advantage and utility of placing a protective liuid` or emulsion in an exposed zone orarea without lowering the effective depth of the tubing lies inthe facty that the work is performed before removing the Christmas tree from the well-headand in. stalling .the'blowout preventers. This provides protection from blowouts which might occur while lowering the tubing prior to circulating the well. Furthermore, the

present invention saves operational time and expense as compared with the use of a tubing extension to increase the effective depth of the tubing. In each instance the placement of the protective fluid in the area or zone to be protected prior to filling and circulating the well with the usual working fluid for blowout protection hask the advantages of (a) where salt water is used as a working fluid, the fluid prevents loss of salt water to the formation during the circulating operation, and (b) in the case of the use of mud as the working fluid, preventing the mud from contacting the exposed productive horizon which would tend to plug the formation material in the horizon and reduce its subsequent productivity. Furthermore, by using the protective fluid subsequent cementing or sand control operations in the protected area are facilitated and make possible effective treatment in such operations.

In the practice of the present invention, a protective uid of the type illustrated before is introduced or pumped into the` tubing in a small quantity, which may range from about l to about barrels and may be followed by pumping the usual workover or well servicing uid to displace the protective uid out of kthe bottom of the tubing` By using a protective uid heavier than the well fluids in the well bore prior to conducting a well servicing or well workover operation, the well fluids in the well bore be low the bottom of the tubing may be displaced into the zone open to production by the differential weight of the protective uid. Thus, the protective iluid, which has differential pressure to displace the cohesive body from the protected area and up the repaired tubing, for example; following which production of valuable hydrocarbon fluids from the well is obtained. The cohesive bodymay also be removed without disturbing the tubing by swabbing or lightening the fluid in the well such as by gas lift, and

the like.

The present invention will be further described and illustrated by reference to the drawings in which:

Figs. 1 to 3 illustrate a step-wise operation in accordance with the present invention.

Referring now to the drawing in which identical numerals will be employed to designate identical parts, numeral 11 designates a well bore drilled from the earth surface 12 to penetrate a plurality of sub-surface earth intervals 13, 14, 15 and 16, among which selected of the intervals may be productive of hydrocarbon and other intervals may be non-productive. For example, intervals 13 and 16 maybe productive ofhydrocarbon while intervals 14 and 15 may be non-productive. In any event, a casing 17 is arranged in the well bore 11 and is cemented in place employing the usual` practice with cement 18 in the well bore 11. The casing 17 has been perforated in the horizon 16 to form perforations 19 through the casing 17, the cement18- and into the formation material in interval 16. In the practice of the present invention holes or leaks lsuch as 20 may have developed in the tubing 21 and itis desired to repair or replace the tubing 21. The

` tubing 21 is supported in a well head 22 and in the casing the property of forming a cohesive body, settles to the area in the producing zone without intermingling or mixing with kthe welluids.` The protective iluids have the characteristic of a low ltration or tluid loss and do not enter the formation following the well fluids. On opening the casingltubing annulus connection at the well head, the well uids in the annulus are circulated or displaced back tothe surface as they are displaced by pumping of the servcingor workover fluids into the tubing. In this manner, oil and gas in the annular space are removed and the well bore above the protective fluid is completely filled with the working fluid for blowout protection during subsequent operations.

The working fluid is suitably oil, salt Water, which may contain a weighting agent, or drilling tluids such as drilling mud, or the like. The important consideration of using the protective Huid in the manner indicated is that the exposed area of the perforations is not contacted with the workover tluid. In addition, the employment of the protective fluid in the manner indicated has other advantages, among which is its property of, forming and remaining in a cohesive mass. This is an important consideration since many well servicing or work-over operations are occasioned or caused by the presence of leaks in the tubing such as actual holes in or around the threads of the couplings. In view of the protective fluid having its property of cohesiveness by virtue of its viscosity and gel strength and diierential Weight advantage, it does not flow out of small holes in the tubing and substantially lay-passes small holes or leaks in the tubing as a slug or body. Furthermore, it is not circulated back to the surface from the level at which a leak may occur and it does not circulate up the annular space between the tubing and the wall of the well or casing. Additionally, by virtue of a differential pressure between the tubing and the casing-tubing annulus the protective uid may suitably till any openings or leaks in a tubing intermediate the ends of the tubing arid allow subsequent circulation of worlcover fluids without being by-passed through the leaks.

After a workover operation has been employed in a well in accordance with the present invention, the workover fluid may be replaced by lighter fluid, such as fresh water which lightens the column in the well and provides a pressure differential into the well bore which will cause 17 by means of a tubing head and hanger 23. A ange 25 closes the casing-tubing annulus26 and the tubing 21 extends through the flange 2S and is closed by a valve l 26, and is provided with a lateral conduit 27 controlled by valve 28.

Since it is desired to repair the tubing 21, the perforations 194 are protected from contact with the fluid which is used to control the well with a protective fluid having the characteristic or property of forming a cohesive mass; the protective iluid is introduced into the tubing through conduit 27 controlled by valve Z8 and flowed or pumped downwardly through the tubing 21. The pumping may be conducted by first introducing or pumping the emulsion into the tubing followed by the workover or servicing fluid, which may be oil, fresh or salt water, and the like, into the tubing. As the emulsion flows downwardly through the tubing it may suitably ll the leaks or holes 20 as it issues from the lower open end 29 of the tubing as an elongated body 30 `and settles'or flows downwardly to fill the casing in the region of the perforations 19. It is to be noted that the elongated body 30 does not intermingle or mix with the well fluids filling the well casing which are displaced up the annulus 26 and from the casing by means of conduit 31 controlled by valve 32,.

After the cohesive body 30 has filled the casing adja-A cent the perforations 19 it may be desirable to circulate the well uids which suitably may contain gas and may be composed of oil, water and gas from the well. This may be done by continuing the pumping of the workover fluids into the tubing through conduit 27 and out through the open end 29 of the tubing. Since the perforations or leaks 20 in the tubing 21 may be lled with the protective fluid the workover fluid ows up the annulus 26 and removes substantially all of the well uids from the well. Since the workover fluids have sufficient weight to overcome the formation pressure of formation 16, the flange 25 may be unbolted and the leaking tubing 21 may be pulled and replaced with a nonleaking tubing 21a and the Christmas tree replaced such as shown in Fig. 3, the blowout preventers as illustrated by numer al 33 in'Fig. 2 having been placed on the head 22 prior to removal of the tubing 21 and hanger 23, if desired. Thereafter the valve 32 remains closed and production is had thro-ugh the tubing 21a by lightening the column of the workover fluids in the well such as by introducing tubing by using a tubing extension member.

55 aslighter fluid into the-well .'or'by swabbing or gas-lift, and the like. The body of protective fluid 30 is displaced up Ithrough the open end 29 of tbe repaired tubing 21a followed by hydrocarbon fluids from the formation 16, it being Anoted that the perforations 19 have been protected at alln'mes against contact with drilling mud or with vworkover fluids.

Advantageously, the present invention is applicable .to the so-called permanent well completion techniques ,wherein the tubing is arranged permanently in place once in the economic lifetime of the Well and subsequent operations are conducted with the tubing maintained permanently in place. Thus, in acordance with the present invention, by virtue of the property of the protective fluid, it is possible to locate the protective fluid without lower- -ing the tubing and extending the effective length of the In other Words, the protective fluid has sufficient cohesiveness that it resists admixture with well fluids andthe like and does not :become displaced up the annulus and from the well.

Ther present invention has been usedsuccessfully in several crude oil producing fields. In one operation in the Gulf Coast of Texas it Was necessary to repair a .leaking tubing, the lower end of which was about 300 Afeet above the producing interval to be protected. In

this operation the protective fluid was poured or pumped into the tubing at the surface following which salt water was pumped downwardly through the tubing until the well fluids in the tubing-casing annulus -ceased to contain yoil and only salt water was being returned. The protective fluid did not flow up the annulus and was spotted or located in the area in the well from which hydrocarbons had been produced. Thereafter, with the vWell under control, the well flange was unbolted and the tubing pulled, repaired, and then replaced. The well was then restored to prducing hydrocarbons as has been described. moving the well fluids from the well was from about l2 to 18 hours whereas prior to the present invention an `Under such conditions the protective fluid is pumped or poured into the tubing and displaced out the bottom of the tubing without any subsequent circulation of the workover fluid. In this manner the protective fluid displaces the well fluids ahead of the protective fluidbut yet maintains a sufllciently heavy column of fluid in the well to protect against a blowout when the well is open prior to placement of the repaired tubing and the blowout preventers or conducting of another operation.

Besides the several enumerated advantages of the present invention, the invention is also of utility in that amethod is provided wherein loss of salt water, where salt Water is the workover fluid, to the formation is prevented.

The present invention, while specifically illustrated with reference to repairing leaking tubing, is applicable to any operations where protective fluid is employed to protect an exposed area or interval following which it is desirable to conduct another operation in the well above the productive interval without moving the tubing. Examples of other operations are installation or repair of gas lift valves, retrievable or otherwise, subsurface pumps, either hydraulic or rod, subsurface chokes, casing leak repairs, replacement of surface control equipment, re-

In these operations the time involved for re.

pair.: of casing; and replacement `of' tubing/packers; 'and the like.

.Itvr is contemplated .that operations as mentioned fand .described before may be conductedin wells completed in a plurality of zones where the zones. are produced simultaneously :or selectively either with the fluids from the severalzones being commingled or ,maintainedzseparatefrom each other. For example, where a well is equipped for dualV completion with parallel strings of tubing either concentrically arranged or in side-by-side relationship, it may be desirable to perform an operation as. described and, in that event, one or both of the exposed zonesV may be protected with the protective `fluid While the repair or workover operation is, carried out without moving the tubingi'or extending its effective length.

While the invention has been described and illustrated for Vuse' in a perforated-casing,this is given by way of ,illustration and not by way of limitation inasmuch: as the invention may be practiced in open hole below a cased and tubed well or in a well where a Itubing is not used-.orwhere a :tubing is subsequently run.

fAlso, While small amountsof the protective fluid in an amount from about l to about.20 barrels have been described, lesser or larger amounts may be used. For example, about 200 to 400 barrels of fluids usually ll wells drilled to about 5,000 to about 10,000 feet range dependingon the size of the casing. An amount of protective fluid ymay be used ranging from about 0.5 to l0 percent by volume based on the amount of fluid required to fill the Well.` Some adjustment in 'amounts may be .desirable where alongexposed area existsin thexwell.

The naturev and objects, of the present inventionhav- `ing been completely described and illustrated, what we wish to claim as new and `useful and to secure by Letters Patent is:

l. A method for protecting an exposed area in a well having a tubing arranged therein with its lower open end -maintained at a level a substantial distance above said area, said well being filled with Well fluids, which comprises introducingl into said tubing at the well head a stable low fluid loss fluid selected from the group consisting of gels Vand emulsions of an oily phase and an aqueous phase containing an emulsifying agent, said low fluid loss fluid being free of solids and constituents which might damage said exposed area, having a controllable density by having a Weighting agent dissolved in one of said phases, and having a Weight at least equal to the weight of a workover fluid for the Well and said low fluid loss fluid also having the property of forming a cohesive body, and flowing said low fluid loss fluid out the lower end of said tubing free of any confining channel to form said cohesive body extending in elongated form from said lower end of the tubing through said well fluids separate and distinct from said well fluids to and filling said area, discontinuing introduction of said low fluid loss fluid, and then introducing said workover fluid into said tubing lat the well head and flowing said workover fluid out the lower end of said tubing whereby said well fluids are displaced from the well up. the annular space between the tubing and the wall of the well, said cohesive body remaining in and protecting said exposed area during displacement of said well fluids while maintaining said tubing with its lower end at said level.

2. A method for protecting an exposed area in a well having a leaking tubing arranged therein with its lower vopen end maintained at a level a substantialv distance aqueous pbase containing an emulsifying agent, said low fluid loss fluid being free of solids and constituents which might damage said exposed area, having a c'ontrollabley density by having a weighting agent .dissolved in one of said phases,`and having a weight at least equal to the weight of a workover fluid for the well and said low uid loss lluid also having the property of forming a cohesive body, and owing said low lluid loss fluid out the lower end of said tubing free of any conning channel to form said cohesive body extending in elongated form from said lower e'nd of thetubing through said well lluids separate and distinct from said well fluids to and filling said area,` discontinuing introduction of said low uid loss iluid, then introducing said workover fluid -into said tubing at the well head and flowing said workover fluid out the lower end of said tubing whereby said well fluids are displaced from the well up the annular space between the tubing and the wall of the well, said cohesive body remaining in and protecting said exposed area during displacement of said well uids while maintaining said tubing with its lower end-at said level, re-

`moving the leaking tubing from the well andreplacing same with a tubing free of leaks, removing said cohesive body from said area, and'then producinghydrocarbons from said area.

3. A method for protecting an exposed areain a well having a leaking tubing arranged therein with its lower open end maintained at a level a substantial distance above said area, said well being filled with well fluids, which comprises introducing into said tubing atthe well head a stable low luid loss fluid selected from the group consisting of gels and emulsions of an oily phase and an aqueous phase containing an emulsifying agent, said low liuid loss fluid being free of solids and constituents which might damage said exposed area, having a controllable density by having a weightingagent dissolved in o'ne of said phases, and having a weightat least equal to the weight of a` workover fluid for the well and said low fluid loss lluid also having the property of forming a cohesive body, and flowing said low fluid loss fluid out the lower end of said tubing free of any conning channel to form said cohesive body extending in elongated form from said lower end of the tubing through said well iuids separate and distinct from said well iluids to and filling said area,` discontinuing introduction of said low uid loss fluid, then introducing saidworkover uid free of gas into said tubing at the well head and owing said workover uid out the lower end of `said tubing whereby said `well iuids are displaced from the well up the annular space between the tubing and the Wall of the well, said cohesive body remaining in and protecting said exposed area during displacement of said well fluids while maintaining said tubing with its lower end at said level, repairing the leaking tubing, removing said cohesive body from said area, and then producing hydrocarbons from said area.

4. A method for protecting an exposed area inawell having a tubing arranged in a perforated casing with its lower open end maintained at a level a substantial distance above the perforations, said well being filled with well iluids, which comprises introducing into said tubing at the well head a stable low l'luid loss liuid selected `from the group consisting of gels and emulsions of an oily phase and an aqueous phase containing an emulsifying` agent, said low lluid loss iluid being free of solids and constituents which might damage said exposed area, having a controllable density by having a weighting agent dissolved in one of said phases, and having a weight at least equal to the weight of a workover iluid for the well and said low liuidloss fluid also having the property of forming a cohesive body, and flowing said low fluid loss uid out the lower end of said tubing free of any conning channel to form said cohesive body extending in elongated form from said lower end of the tubing through said Well fluids separate and distinct from said Well iluids to and lling said casing in the region of the perforations, discontinuing introduction of said low uid loss fluid, and then introducing said workover fluid into said tubing at the well head and liowing said workover fluid out the lower end of said tubingwhereby said well fluids are displaced from the well up the annular space between the tubing and the wall of the well, said cohesive body remaining in said region and protecting said perforations during displacement of said well fluids While maintaining said tubing with its lower end at said level.

5. A method for protecting an exposed area in a well having a leaking tubing arranged within a perforated casingwith its lower open end maintained at a level a substantial distance above said perforations, said well being iilled with Well fluids containing gas, which comprises introducing into said tubing at the well head a stable low `iluid loss emulsion of an oily phase and an aqueous phase containing an emulsifying agent, said emulsion being free of solids and constituents which might damage said exposed area and being of a controllable density by having a weighting agent dissolved in one of the phases of said emulsion and said emulsion also having the property of forming a cohesive body, and llowing said emulsion out the lower end of said tubing free of any confining channel to form said cohesive body extending in elongated form from said lower end of the tubing through said well lluids separate and distinct from said well fluids to and lling said casing in the region of the perforations, discontinuing introduction of said emulsion,`th`en introducing a fluid free of gas into said tubing at the well head and flowing said uid free of gas out the lower end of said tubing whereby said well iiuids are displaced from the well up the annular space between the tubing and the wall of the well, said cohesive body remaining in said region and protecting said perforations during displacementof said well fluids while maintaining said tubing with its lower end at said level, repairing the leaking tubing, removing said cohesive body, and then producing hydrocarbons through said perforations.

6. A method for protecting an exposed area in a Well having a tubing arranged therein with its lower open end maintained at a level a substantial distance above said area, said well being filled with well fluids, which comprises introducing into said tubing at the well head a stable low iuid loss emulsion of an oily phase and an aqueous phase containing an emulsifying agent, said emulsion being free of solids and constituents which might damage said exposed area and being of a controllable density by having a Weighting agent dissolved in` one of the phases of said emulsion and said emulsion also having the property of forming a cohesive body, and flowing said emulsion out the lower end of said tubing free of any confining channel to form said cohesive body extending in elongated form from said lower end of the tubing through said well lluids separate and distinct from said well fluids to and iilling said area, discontinuing introduction of said emulsion, and displacing said well fluids from the well up the annular space between the tubing and 1the wall of the well, said cohesive body remaining in and protecting said exposed area during displacement of said well lluidswhile maintaining said tubing with its lower end at said level.

7. A method for protecting an exposed area in a well having a leaking tubing arranged therein with its lower openend maintained at a level a substantial distance above said area, said well being lled with well lluids containing gas, which comprises introducing into' said tubing at the well head a stable low uid loss emulsion of an oily phase and an aqueous phase containing an emulsifying agent, said emulsion being free of solids and constituents whichmight damage said exposed area and being of a controllable density by having a weighting agent dissolved in one of the phases of said emulsion and said emulsion also having the property of forming a cohesive body and llowing said emulsion out the lower end of said tubing free of any confining channel to form said cohesive body extending in elongated form from said lower end of the tubing through said well uids separate and distinct from said well uids to and lling'said area, discontinuing introduction of said emulsion, displacing said well lluids from the well up the annular space between the tubing and the wall of the well, said cohesive body remaining in and protecting said exposed area during displacement of said well uids While maintaining said tubing with its lower end at said level, repairing said leaking tubing, removing said cohesive body, and then producing hydro' carbons from said area.

8. A method for protecting an exposed area in a well having a tubing arranged within a perforated casing with its lower open end maintained at a level a substantial distance above said area, said well being lled with well luids which comprises introducing into said tubing at the well head a stable low fluid loss uid selected from the group consisting of gels and emulsions of an oily phase and an aqueous phase containing an emulsifying agent,

said low uid loss fluid being free of solids and constituents which might damage said exposed area, having a controllable density by having a weighting agent dissolved in one of said phases, and having a weight at least equal to the weight o-f a workover iluid for the well and said low uid loss uid also having the property of forming a cohesive body, and lowing said low fluid loss fluid out the lower end of said tubing free of any confining channel to form said cohesive body extending in elongated form from said lower end of the tubing through said well uids separate and distinct from said well fluids to and lling said area, discontinuing introduction of said low iiuid loss fluid, and displacing said well fluids from the well, said cohesive body remaining in and protecting said exposed area during displacement of said well uids while maintaining said tubing with its lower end at said level.

9. A method for protecting an exposed area in a well having a tubing arranged therein with its lower open end maintained at a level a substantial distance above said area, said well being lled with well fluids, which comprises introducing into said tubing -at the well head a stable low fluid loss emulsion consisting of an aqueous phase and an oily phase containing a water soluble salt of lignin sulfonic acid emulsifying agent, said low iluid loss emulsion being free of solids and constituents which might damage said exposed area, having a controllable density by having a weighting agent dissolved in one of said phases, and having a weight at least equal to the weight of a workover uid for the well and said low uid loss emulsion also having the property of forming a cohesive body, and iiowing said low fluid loss emulsion out the lower end of said tubing free of any confining channel to form said cohesive body extending in elongated form from said lower end `of the tubing through said well fluids separate and distinct from said well iluids to and filling said area, discontinuing introduction of said low fluid loss emulsion, and then introducing said workover uid into said tubing at the well head and flowing said workover fluid out the lower end of said tubing whereby said well fluids are displaced, said cohesive body remaining in and protecting said exposed area during displacement of said well fluids while maintaining said tubing with its lower end at said level.

10. A method in accordance with claim 9 in which the oily phase of the emulsion comprises tetrachloroethylene. i

1l. A method in accordance with claim 10 in which one of the phases of the emulsion contains a corrosion inhibitor.

References Cited in the file of this patent UNITED STATES PATENTS 2,426,317 Menaul Aug. 26, 1947 2,749,989 Huber June 12, 1956 2,772,738 Tausch Dec. 4, 1956 2,793,188 Swain et al, May 21, 1957 

